Tennis courts are relatively large. Tennis players and instructors use ball retrievers to minimize ball gathering time. Retrieving devices are utilized to collect dispensed tennis balls and to discharge them into carts, hoppers or ball machines.
Stap patented a portable tennis ball retriever in 1968, U.S. Pat. No. 3,371,950. He describes a tennis ball retriever and storage unit comprised of an upright wire basket with a top opening, a handle with a round grip mounted above the top opening, a retrieving bottom grate including parallel rods spaced from each other a distance smaller than a tennis ball's diameter, so as to define the space through which squeezed balls pushed against a tennis court flat surface enter and remain in the retriever. Retrieving procedure consists of placing the basket over a ball or a few balls, pushing it down and lifting the basket up with retrieved balls inside. The most recently retrieved balls push the previously retrieved balls up towards the top of the basket. This sequence is repeated until the basket gets full. Discharging procedure comprises tipping of the receptacle out of the upright position.
This compact wire basket has a simple prism shape. It is easy to use and inexpensive to manufacture. The device is light, reliable, and does not require bending over during the ball retrieval process.
When a considerable amount of balls is collected in the basket, it is difficult to push the basket down and collect additional balls. This is caused by the compression of soft tennis balls in between the parallel vertical side walls. Side wall reaction forces appear as a result of an insertion of incoming balls in-between balls previously residing in the basket. The large coefficient of friction between tennis balls contributes to significant resistance of the balls internal movement. An extensive friction force negatively affects retrieving and discharging procedures. The round grip handle does not provide the needed leverage to keep the basket from twisting and turning while retrieving balls. It requires extra time to accurately place the container 20 in the retrieving position. As a result, the basket with round grip handle is not efficient in the retrieval process.
Christina E. Turdo patented a nestable ball retrieval and storage device in 2012, U.S. Pat. No. 8,141,919. She describes a tennis ball retriever utilizing a similar structure, and similar retrieving and discharging procedures as the wire basket patented by Stap, but this receptacle includes slanted side walls and has pyramidal frustum shape. The receptacle wall structure has an open top and converges inwardly from the open top to the bottom grate to establish a tapered cavity.
This wire basket is easy to use. It is light, reliable, and does not require bending over during the ball retrieval process. The resistance force of balls entering and exiting the receptacle is reduced. The tapered down cavity side walls generate the resultant reaction force directed upwards. It eases balls movement toward the open top.
However, the tapered receptacle has some disadvantages in comparison with the prism shaped retriever. The tapered receptacle's bottom grate size has to be considerably smaller than the top size which is predetermined by storage ability. The small size bottom grate would allow retrieving fewer balls at once. Moreover, the tapered retriever is inconvenient for collecting balls located next to an obstacle like a fence or a net, because when the top of the retriever is flush with such an obstacle, the bottom is tapered away. In such situations, the bottom edge cannot get behind the ball to retrieve it. These facts diminish the tapered receptacle's efficiency. In addition, this nestable ball retrieval and storage device has the same round grip handle issue as the retriever patented by Stap.
There are more retrievers with a tapered cavity described in U.S. Pat. Nos. 4,412,697; 6,945,578; 6,354,643; 6,302,460.
Commercially available light and compact wire baskets utilized as portable tennis ball retrievers have a pyramidal frustum shape and a handle with a round grip. They have a logo plate welded to a side wall. This plate is an obstruction in ball retrieving and discharging procedures. Furthermore, a logo plate made from thin sheet metal might have sharp edges. It is unsafe to use such devices especially for children, because their hands often go inside the device to speed up ball discharging. Commercially available lightest wire basket has the side wall with only twelve vertically oriented wires. It is compact, but has a small capacity. This retriever has a double rod bottom structure, which does not allow use of plastic rollers to protect the tennis court surface and the basket's integrity.